I've an older one, an inexpensive thing, that sort of looks like the pic I snipped, below. Basically it is a blower with a 4" outlet on which is fitted the bag, and the inflow is centered on the impeller's axis.
I am wondering what it might take to use the blower part as the core of a new setup, one with an intermediate can with shop-made cyclone top, the output going into a stack with filter atop and bag below.
Or am I just being a cheap guy.